How do rates of dementia vary across England? Over 400,000 people have been diagnosed with dementia. Prevalence of the disease is closely associate with age. This means that we would expect areas with an older population to have a greater number of people living with dementia. This blog looks at how we might account for this effect, and what the resulting data tells us about variation in dementia across England.

Diagnosing dementia

Over 400,000 people have been diagnosed with dementia in England. It’s estimated that around two-thirds of those living with dementia have been diagnosed. Around 7 in 10 people with dementia are aged 80 or over, while around 7% are aged under 65.

The percentage of people in each age group diagnosed with dementia is shown in the following chart.

Identifying ‘crude’ rates of dementia

Using NHS Digital’s data we can estimate which parts of the country have higher and lower rates of diagnosed dementia.

However, when we calculate dementia rates, we find that the highest rates are typically found in those areas that have a higher proportion of people in older age groups. Given that we already know that older people are much more likely to have dementia, this isn’t too informative. The map of ‘crude’ dementia prevalence (see below) looks similar to a map of constituencies with an older age profile.

(For full constituency data, see our downloadable tables.)

Taking into account age differences

However, we can take this into account by ‘age-standardising’ the data. To do this, we estimate what dementia rates would be if every constituency had the same proportion of older and younger people as the national average. This lets us estimate which areas have higher rates of dementia than we should expect. Even if an area has relatively few people diagnosed with dementia, it might still have higher rates than expected if that its population is younger than the national average. Similarly, even if an area has lots of people diagnosed with dementia, it might still have lower rates than expected if its population is much older than average.

The difference between the ‘crude’ rates and the age-standardised rates is shown in the maps below, and the constituencies with the highest rates on the age-standardised measure are shown in the chart.

On this measure, areas in the north of England have higher-than-expected rates of dementia. There is also a relationship with deprivation levels – areas with a higher number of deprived households tend to have higher age-standardised rates of dementia.

Remember that these figures only account for people who are diagnosed with dementia. Differences between areas might reflect differences in diagnosis rates rather than differences in the number of people with dementia.

Find out more

More information on this analysis is contained in our briefing paper.

The data on dementia which underlies this work is published by NHS Digital.

The Alzheimer’s Society discuss risk factors for dementia, which may help to explain some of the variation described above.

Picture credit: Nurse Holding Elderly Patient’s Hand, by PortaldelSur ES; Creative Commons Attribution 2.0 Generic (CC by 2.0)